The present invention relates to a binder for a polydiene composite propellant, particularly a polybutadiene composite propellant.
Recently, as a binder for a polybutadiene propellant, particularly a propellant using a small amount of a binder, a binder consisting mainly of a reaction product of a hydroxyl terminated polybutadiene and a diisocyanate has been noticed. The inventors have already proposed a binder which can provide uniform physical properties and prolong the pot life and therefore improve the producibility and physical properties of a propellant, which is produced by reacting a polydiene glycol having a hydroxyl group number of 1.8-2.1 and a number average molecular weight of 1,000-5,000, with a trifunctional cross-linking agent, a diisocyanate and bifunctional chain extender (see Japanese Patent Application No. 123,345/78, filed on Oct. 6, 1978). When a propellant using a small amount of a binder is produced, the viscosity of the binder is an important factor, so that the production must be carried out in one-shot process and therefore the chain extending reaction and the cross-linking reaction should be controlled by properly selecting the combination of the compounding agents but in the above described binder system, the pot life becomes long and the mechanical properties are improved, but the reactivity of the diisocyanate to the polydiene glycol and to the trifunctional cross-linking agent is different and the distribution of the cross-linked structure is apt to become nonuniform and the curing time becomes too long and the cost for controlling the temperature in chamber becomes higher. The pot life is substantially determined by the reaction of the polydiene glycol with the diisocyanate but this reaction is carried out at such a smooth rate that no catalyst is necessary. On the other hand, the curing time is substantially determined by the reaction of the trifunctional cross-linking agent with the diisocyanate but if it is intended to shorten the curing time, a catalyst is necessary and this catalyst influences the reaction of the above described polydiene glycol with the diisocyanate and the pot life tends to become short. This is due to the addition of the trifunctional cross-linking agent.